Post-space flight orthostatic hypotension/intolerance occurs in 25 to 66 percent of crew members upon returning to a 1 G environment. The mechanism(s) causing this response are not completely understood. Identification of countermeasures to reduce the incidence of orthostatic intolerance associated with space flight is paramount to NASA's mission. One such countermeasure may be skin surface cooling. In light of this, three specific objectives will be accomplished by the proposal work: 1) Identify an optimal skin surface cooling paradigm that causes the largest increase in autonomic responses (i.e. stroke volume, blood pressure, sympathetic nerve activity, etc.) without causing shivering or altering motor function. 2) Identify the mechanisms by which skin surface cooling increases the aforementioned autonomic responses resulting in improved tolerance to orthostatic stress. 3) Identify whether skin surface cooling is an effective countermeasure to improve orthostatic tolerance in men and women following simulated microgravity exposure using the head-down tilt bed rest model. Upon completion of the proposed studies important information will be provided that will be beneficial for both operational and safety concerns for astronauts, as well as to individuals who suffer from idiopathic orthostatic intolerance.